In plastic container production processes a preform is normally produced first, the preform comprising the amount of material required for the finished container and preferably also the finished neck provided with a thread as well as possibly a collar positioned below the thread, the rest of the preform being, however, smaller and having thicker walls than the finished container. This preform is preferably produced by injection molding. The preform is then inserted into a blow mold and deformed by pressure gas and, where appropriate, mechanical stretching so as to form the finished container. Between the step of injection molding of the preform and the step of blow molding, the preform is preferably heated once more. Inserting the preform into the blow mold with a specific orientation may be advantageous or necessary for a great variety of reasons. This may, for example, become necessary for containers in the case of which anon-rotationally symmetric container, e.g. a container having an oval cross-section, is formed from a rotationally symmetric preform. Here, it will be advantageous to heat the preform areas which are to be stretched more intensively, i.e. the outer areas of the oval, to higher temperatures than the other areas, so that a substantially identical wall thickness will be accomplished everywhere. In this case it will be necessary to insert the preform into the blow mold with an orientation that is exactly adapted to the selectively different degrees of heating. However, it often happens, for a great variety of reasons, that the orientation of the preform changes prior to or during insertion of the preform into the blow mold.
In order to avoid this, many possibilities have been suggested. EP 1 279 477, for example, shows a heating station integrated in the blow molding station and followed by a position regulator which corrects the positions of the preforms once more before the actual blow molding process is carried out. The position regulator includes a sensor which discerns an orientation mark on the preform and detects whether the latter is at a predetermined rotary angle position. If this is not the case, the preform holder, which consists here of a mandrel to which the preform is attached with its opening facing downwards, is driven by a motor via a rack/gear ring transmission. This way of correcting the orientation is comparatively complicated and necessitates electronic control.
Another possibility of making the rotary angle orientation of the preform more uniform or of correcting it is known from EP 1 261 471. In the case of this structural design, the blow mold comprises a ripping device which is inserted into the neck area of the preform within the blow mold and prior to the blow molding process. Via a sensor device, e.g. an optical device, an orientation mark on the preform is detected and the position thereof determined. If this position does not correspond to the predetermined rotary angle position of the preform, the gripping device is rotated via a motor and a pinion/gear transmission. Also this necessitates a comparatively great expenditure.
Another possibility of correcting the orientation can be gathered from DE 196 47 260 A1. In this case, the rotary angle is adjusted, prior to heating the preform, by rotating a holder to which the preform is attached upside down. The neck area of the container is provided with two diametrically opposed projections defining a stop for two adjustment fingers that move parallel to one another and in opposite directions. The adjustment fingers move on both sides over the neck area such that their end faces are diametrically opposed to one another. Subsequently, the carrier is rotated through a rack/gear ring transmission until the closest stop comes into contact with the end face of the adjustment finger. Also this solution is comparatively complicated and, if at all, only suitable for coarse adjustment.